This application claims the priority of European patent application No. 00 109 302.0, filed Apr. 29, 2000, the disclosure of which is incorporated herein by reference in its entirety.
The present invention concerns primers for the improvement of the adhesion of plastics that are difficult to bond or seal, in particular of polyolefinic thermoplastics with one component or two component adhesive systems.
Primers, also referred to as activators or adhesion promoters, are applied where the used adhesive does not achieve any, or only limited, adhesion to the substrate. Thereby, the adhesive system consisting of pre-treatment (primer) and adhesive are adapted to each other and to the substrate. Such primers can be physically hardening or chemically cross-linking. Pre-treatment (primer) systems for plastics such as e.g. polypropylene, polyethylene, EPDM (ethylene propylene diene terpolymers), polyamide, ABS (acrylonitrile butadiene styrene copolymers) etc., or anti-scratch treated plastics, such as e.g. polydimethylsiloxane coated polycarbonate, are known and described in patent documents.
According to EP 0 409 198, after the application of a primer comprising silyl-functionalized fumarates, the polyolefin must be attached thereto by (partial) melting.
In WO 92/09669 polyolefine primers are disclosed that comprise ethylene diamine derivatives and that in particular are suitable for cyanoacrylate adhesives.
EP 0 295 930 discloses a primer comprising diazobicyclo compounds or triazabicyclo compounds suitable for cyanoacrylate adhesives. Said primer does not form a film and therefore only results in a minor improvement of the adhesion; furthermore, said primer is unsuitable for adhesives that are less rigid then cyanoacrylate adhesives.
In EP 0 703 285 a mixture consisting of chlorinated polyolefin and flexibilized epoxy resin is disclosed as primer for polyolefins. Since said primer is not cross-linking, its heat stability is insufficient. The epoxy resin furthermore has a low affinity to polyolefins. In addition, the presence of chlorine is critical in view of legal regulations.
In the patent documents JP 3 239 761 or JP 62 095 326, respectively, reaction products of hydrogenated polybutenediol with polyisocyanates are desdribed. The low solubility of the hydrogenated polybutadiendiol in a solvent, however, affects the productivity, and because of separation and gel formation the storage stability is limited.
Hence, it is a general object of the invention to provide a primer for the improvement of the adhesion between polyolefinic plastics and adhesives or sealants, respectively, that overcomes the above described disadvantages.
Said goal has been achieved by providing a primer comprising a polyol provided with reactive terminal groups, whereby said polyol comprises hydrogenated polyisoprenediol.